Acute Angle
An angle that measures greater than 0 and less than 90.
Adjacent Angles
Two angles in the same plane with a common vertex and a common side, but no common interior points.
Angle
A figure formed by two rays with a common endpoint.
Angle Bisector
A ray that divides an angle into two congruent angles.
Area
The number of nonoverlapping unit squares of a given size that will exactly cover the interior of a plane figure.
Base
The base b can be any side of a triangle. The best side to use for the base is the one opposite the vertex used when finding the height.
Between
Given 3 points A, B, and C,
B is between A and C if and only if
all 3 of the points lie on the same line.
Bisect
To divide into two congruent parts.
Circumference
The distance around the edge of a circle.
Circumference = (2)(?)(radius)
Collinear
Points that line on the same line.
Complementary Angles
Two angles whose measures have a sum of 90 degrees.
Congruent Angles
Angles that have the same measure.
Congruent Segments
Two segments that have the same length.
Construction
A mathematically precise figure that has been created using methods such as a compass and a straightedge, geometry software, or paper folding.
Coordinate
A number that identifies the location of a point on a number line. On the coordinate plane, the x and y-coordinates are used. In 3D space use 3 coordinates (x,y,z).
Coordinate Plane
A plane that is divided into four regions (quadrants) by a horizontal line called the x-axis
and a vertical line called the y-axis.
Coplanar
Points that line in the same plane.
Degree
A unit of angle measure; one degree is 1/360 of a circle.
Diameter
A segment that has endpoints on the circle and that passes through the center of the circle; also the length of that segment. Diameter = (2)(radius)
Distance
(On the Number Line) The absolute value of the difference of the coordinates of the points.
(Coord. Plane) D = sqrt[ (x2 - x1)^2 + (y2 - y1)^2 ]
Endpoint
A point at the end of a segment,
or the starting point of a ray.
Exterior of an Angle
The set of all points outside the an angle.
Height
The length of an altitude of a figure.
Hypotenuse
The side opposite the right angle angle in a right triangle.
Image
A shape that results from a transformation of a figure known as the preimage
Interior of an Angle
The set of all points between the sides of an angle.
Legs of a Triangle
The two sides of the right triangle that form the right triangle.
Length
The distance between two endpoints
of a segment.
Line
An undefined term in geometry, a line is a straight path that has no thickness and extends forever.
Linear Pair
A pair of adjacent angles whose noncommon sides are opposites rays. The sum of the angles in a linear pair is 180 degrees.
Measure of an Angle
Angles are measured in degrees.
Obtuse Angle
An angle that measures greater than 90 degrees and less than 180 degrees.
Opposite Rays
Two rays that have a common endpoint and form a line.
Perimeter
The sum of the side lengths of a closed plane figure.
Plane
An undefined term in geometry, it is a flat surface that has no thickness and extends forever.
Point
An undefined term in geometry, it names a location and has no size.
Postulate
A statement that is accepted as true without proof.
Preimage
The original figure in a transformation.
Radius of a Circle
A segment whose endpoints are the center of a circle and a point on the circle; the distance from the center of a circle to any point on the circle.
Ray
A part of a line that starts at an endpoint and extends forever in one direction.
Reflection
A transformation across a line of reflection,
the l.o.r. is the perpendicular bisector of each segment joining each point and its image.
Right Angle
An angle whose measure is 90 degrees.
Rotation
A transformation about the point P, known as the center of rotation, such that each point and its image are the same distance from P.
Segment of a Line
A part of a line consisting of two endpoints and all points between them.
Segment Bisector
A line, ray, or segment that divides a segment into two congruent segments.
Straight Angle
A 180 degree angle.
Supplementary Angles
Two angles whose measures have a sum of 180 degrees.
Transformation
A change in the position, size, or shape
of a figure or a graph.
Translation
A transformation that shifts or slides every point of a figure or graph the same distance in the same direction.
Undefined Terms
The undefined terms in geometry are point, line, and plane.
Vertex of an Angle
The common endpoint of the sides of the angle.
Vertical Angles
The nonadjacent angles formed by two intersecting lines.
Pi
The ratio of the circumference of a circle to its diameter, denoted by the Greek letter ? (pi). The value of pi is irrational, often shortened to 3.14 or 22/7 .
Midpoint
The point that joins the segment into two congruent segments. If A(x1,y1) and B(x2,y2), then midpoint M[ (x1 + x2) / 2 , (y1 + y2) / 2 ] ) .
Postulate 1-1-1
Through any two points there is exactly one line.
Postulate 1-1-2
Through any three noncollinear points there is exactly one plane containing them.
Postulate 1-1-3
If two points lie in a plane, then the line containing those points lies in the plane.
Postulate 1-1-4
If two lines intersect, then they intersect in exactly one point.
Postulate 1-1-5
If two planes intersect, then they intersect in exactly one line.
Ruler Postulate
The points on a line can be put into a one-to-one correspondence with the real numbers.
Segment Addition Postulate
If B is between A and C, then AB + BC = AC
Protractor Postulate
Given AB and a point O on AB, all rays that can be drawn from O can be put into a one-to-one correspondence with the real numbers from 0 to 180 degrees.
Angle Addition Postulate
If S is in the interior of ?PQR,
then m?PQS + m?SQR = m?PQR
Pythagorean Theorem
In a right triangle, the sum of the squares of the lengths of the legs is equal to the square of the length of the hypotenuse. a^2 + b^2 = c^2